Supervising system for use in radio transmission

Abstract

A phase shift monitoring system is provided for a mobile communication system which includes a central, or base station, one or more sub-base stations, and a plurality of mobile units. Each sub-base station is provided with a detection means which is operable to transmit an alarm signal to the base station when a predetermined tolerable phase shift is exceeded. The base station includes means for readjusting the transmission timing in order to compensate for the detected phase shift, either automatically or by manual control.

What is claimed is: 
     
       1. A phase shift monitoring system for a mobile communication system having a central station, one or more base stations coupled with said central station through a wired communication link, and a plurality of mobile radio stations linked with said base stations through radio communication links; said base stations, responsive to a command signal supplied from said central station, transmitting from time to time a specific signal common to said mobile radio stations through carrier waves of a common frequency, together with ordinary information signals for communication between said mobile radio stations and said central station, said specific signal having a predetermined repetition rate, characterized in that each of said base stations comprises: means for detecting said specific signal; means for providing a time reference pulse in timed relationship with said information signals; means responsive to said time reference pulse and said specific signal for determining whether the fluctuation in the timing of said specific signal is within a preset tolerable limit; means responsive to said determining means for generating an alarm signal when said preset tolerable limit is exceeded; and means for transmitting said alarm signal to said central station, and means for readjusting the transmission timing of said command signal to compensate for said fluctuation; whereby the specific signals are rendered in phase when transmitted at said base stations through said radio communication so that the interference caused at said mobile radio stations may be minimized. 
     
     
       2. A phase shift monitoring system as claimed in claim 1, wherein said determining means includes a pair of digital comparators operable to produce an output signal if the phase difference between said specific signal and said time reference pulse exceeds a predetermined value, one of said comparators providing an output signal in response to a positive phase difference, and the other of said comparators providing an output signal in response to a negative phase difference. 
     
     
       3. A phase shift monitoring system as defined in claim 2, wherein the outputs of said pair of digital comparators are applied to an OR circuit, said OR circuit producing an output upon either of said comparators producing an output. 
     
     
       4. A phase shift monitoring system as defined in claim 3, wherein the output of said OR circuit is applied to said alarm signal generating means, said alarm signal generating means being operable to produce an output upon receiving a predetermined number of sequential outputs from said OR circuit. 
     
     
       5. A phase shift monitoring system as defined in claim 1, wherein said means for transmitting said alarm signal to said central station comprises gate circuit means operable to insert a 1-bit time reference pulse into the ordinary information signals for communication between said mobile stations and said central station. 
     
     
       6. A phase shift monitoring system as defined in claim 1, wherein said means for readjusting the transmission timing of said command signal comprises manually operated means including a rotary switch, the leads of which are connected to the outputs of a shift register. 
     
     
       7. A phase shift monitoring system as defined in claim 1, wherein said means for readjusting the transmission timing of said command signal comprises a delay circuit at said central station which is adjustable in response to a control means. 
     
     
       8. A phase shift monitoring system as defined in claim 7, wherein said control means comprises means for detecting the amount of the change in the delay time, first memory means for storing said change in delay time, second memory means for storing the previous delay time. microcomputer means for detecting said alarm signal and for adding or subtracting the contents of said first memory means to the contents of said second memory means, whereby the memory of said second memory means is rewritten to contain a new delay time, said delay circuit means being responsive to said second memory means for producing a delayed output, thereby readjusting the transmission timing of said command signal. 
     
     
       9. A phase shift monitoring system as claimed in claim 1, further comprising means for determining the amount of change in the delay time including FIFO memory means receiving as data parallel inputs representing the change in delay caused in the link between the central station and the base station, and microcomputer means responsive to said alarm signal to cause the data stored in said FIFO memory means to be serially transferred through switch circuit means to said central station during the duration of said alarm signal.